Recordable type DVDs (Digital Versatile Disk) include the DVD+R (DVD Recordable) and the DVD+RW (DVD Rewritable), for example. Such recordable type DVDs have high reproducing compatibility with a one-sided single layer read-only type DVD. Thus, much research and development are being conducted to increase the recording speed and recording capacity of such recordable type disk media.
In an optical recording medium that has plural recording layers arranged into a multi-layer structure, a recording/reproducing light directed to a recording layer that is positioned far off with respect the incidence surface of the recording/reproducing light passes through the recording layers positioned closer towards the incidence surface. Thus, in an optical recording medium in which recording is realized by changing the optical characteristics of a recording layer through changing the recording light intensity, the waveform condition and intensity condition for the recording light differs depending on each recording layer. Also, in the case of successively realizing recording on plural recording layers, the waveform condition and the intensity condition for the recording light changes from the initial conditions set at the start of the recording owing to heat generated during the recording of the recording information, for example. Thus, a waveform condition and intensity condition that differ from those for an optical recording medium with a single recording layer have to be set for a multi-layer optical recording medium.
In response to the above considerations, for example, Japanese Laid-Open Patent Publication No. 2002-50053 discloses providing unique information of a data layer such as identification information of the data layer and recording conditions for the data layer in a low reflectance region and a high reflectance region that are alternatingly arranged with respect to an extending direction of the recording tracks to realize a bar code like arrangement.
However, the method disclosed in Japanese Laid-Open Patent Publication No. 2002-50053 is implemented under the premise that the unique information of a data layer may be read without conducting tracking servo, and thereby, an optical pickup may not be able to read the data layer unique information through normal operations. Furthermore, the information region for the data layer unique information, namely, the portion corresponding to the bar code information region cannot be used for information recording, and thereby, recording information density is significantly reduced.